1. Field of the Invention
This invention relates to a walking mechanism for heavy machinery and, more specifically, this invention relates to a walking spud for a drag line excavator or like equipment.
2. Description of the Prior Art
The use of walking mechanisms for limited relocation of heavy equipment, such as drag line excavators, is well known. Such equipment is typically extremely large and heavy so that movement by means such as towing, or on wheels or tracks, is impractical.
Typically, such equipment is constructed on site on a concrete pad adjacent an area to be excavated. One form of drag line excavator comprises a main frame mounted for rotation about a vertical axis on a stationary support frame or tub which rests on the underlying terrain. A long excavating boom supported by the main frame extends from a forward end thereof. When excavation of an area forward of the excavator is complete, the excavator is moved to the rear by means of a walking mechanism comprising a pair of generally vertically spaced hinge and rotatable eccentric crank pins projecting horizontally from each side of the main frame. Mounted on each pair of pins for sliding translational and rotational movement with the crank pin is an upright spud attached at its lower end to a longitudinally extending shoe. Typically, the excavator's center of gravity is disposed forwardly of the spud.
The crank pin is rotated so as to raise and lower the shoe relative to the ground. The crank rotates to move the excavator relative to the shoe when the shoe is pressed against the ground. The crank lifts the shoe (once the excavator sits back on the ground) and moves the shoe back to a new location. During lifting and dragging of the excavator, the weight of the excavator is supported by the spud and shoe so that the excavator is first lifted and then dragged to the rear. As the crank pin cycle of rotation is completed, the supporting frame is lowered as the shoe is lifted from the terrain.
One widely used form of prior walking mechanism is described in Page U.S. Pat. No. 2,164,120 issued June 27, 1939, the details of which are incorporated herein by reference. In prior walking mechanisms of the type described above, the horizontal axis of the hinge pin, the axis of eccentricity of the crank pin and the point of attachment of the spud to the shoe defined a generally vertical line. In prior walking drag lines, the forward end or toe of the excavator's supporting frame applied a bulldozing effect to the underlying terrain during walking, thereby building up a mound of earth beneath the tub. This bulldozing effect was quite substantial, since about 1/3 or more of the excavator's weight was concentrated at the toe of the tub in prior excavators during the walking movement. The resulting build-up of earth below the tub is undesirable since it is preferred that the excavator be disposed on a level plane after the walking movement.